#include <stdio.h>
#include <stdlib.h>

/* typical C boolean set-up */
#define TRUE 1
#define FALSE 0

typedef struct StackStruct
{
 int*    darr;  /* pointer to dynamic array  */
 int     size;  /* amount of space allocated */
 int     top;   /* top of stack indicator    */
} Stack;

void init (Stack* s)
{
 s->size = 2;
 s->darr = (int*) malloc ( sizeof (int) * s->size );
 s->top  = 0;
}

void push (Stack* s, int val)
{
  /* check if enough space currently on stack and grow if needed */

  /* add val onto stack */
  s->darr[s->top] = val;
  s->top = s->top + 1;
}

int isEmpty (Stack* s)
{
  if ( s->top == 0)
    return TRUE;
  else
    return FALSE;
}


int top (Stack* s)
{
  return (  s->darr[s->top-1] );
}

void pop (Stack* s)
{
  s->top = s->top - 1;
}

int main (int argc, char** argv)
{
 Stack st1;

 init (&st1);

 push (&st1, 20);
 push (&st1, 30);
 push (&st1, 40);
 push (&st1, 50);
  
 while ( isEmpty(&st1) == FALSE)
   {
    int value = top (&st1);
    printf ("The top value on the stack is %d\n", value);
    pop (&st1);
   }
}